What Is the Impact of Climatic Changes on the Spread of Infectious Diseases?
The distribution of infectious diseases is intricately linked to a range of intricate social and demographic considerations. These factors encompass aspects like access to healthcare services, human population density and its behaviors, water supply systems, waste management, the nature and location of housing, sewage systems, land use patterns, the availability and implementation of vector control programs, irrigation methods, and overall environmental sanitation practices. In addition to these, meteorological elements such as temperature, humidity, and patterns of rainfall also play a pivotal role in influencing the intensity of disease transmission.
The resurgence of infectious diseases in recent times can be primarily attributed to a host of social and demographic factors. These factors include the growth of populations, urbanization trends, immigration patterns, alterations in land utilization and agricultural techniques, deforestation activities, increased international travel, and breakdowns in public health services. Together, these factors contribute significantly to the resurgence of infectious diseases, highlighting the intricate interplay between human activities, environmental dynamics, and disease transmission.
What Are the Types of Infections That Spread Due to Changes in Climate?
1. Water-borne Diseases:
Warmer climatic conditions have the potential to elevate the prevalence of water-borne diseases, which include Cholera and diarrheal illnesses such as salmonellosis, giardiasis, and cryptosporidiosis.
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Diarrheal Illnesses - Diarrheal diseases already impose a significant burden of illness and mortality, particularly among children due to unsafe drinking water and inadequate sanitation primarily contribute to the occurrence of diarrheal diseases; consequently, any reductions in the availability of freshwater resources could likely amplify the occurrence of these diseases. The rapid processes of urbanization, industrialization, population growth, and inefficient water management are already contributing to water scarcity. Climate change is anticipated to compound these water scarcity issues as average annual rainfall decreases across numerous regions.
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Cholera - It is a well-known diarrheal disease transmitted via contaminated water and has afflicted human populations since ancient times. The realization that Vibrio cholera, the bacterium causing cholera, exists in a dormant state between epidemics transformed the understanding of its transmission dynamics. Moreover, there exists a correlation between elevated sea-surface temperatures and the emergence of cholera epidemics, with outbreaks aligning with the seasonal variations in temperature and sea-surface height. Notably, increases in cholera bacterial populations linked to plankton blooms during spring and summer have been observed off the coastlines.
2. Tick and Mosquito Bites:
The lenient winters, premature onset of spring, and elevated temperatures are affording mosquitoes, and ticks extended windows for breeding, disease transmission, and the enlargement of their habitats. In the same timeframe, an additional nine pathogens transmitted by mosquitoes and ticks emerged or were introduced into the United States. Experts are forecasting a sustained rise in tickborne diseases, potentially even worsening over time. Extended and warmer summer seasons have similarly granted mosquitoes a lengthier span for reproduction and disease dispersion.
3. Vector-borne Diseases:
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Malaria - Malaria represents one of the most intricate and critical challenges in the realm of public health. Annually, the global stage witnesses around 400-500 million malaria cases and a grim toll of over a million deaths attributed to malaria. The resurgence of malaria on a worldwide scale can be attributed to a confluence of factors. These include the rise of resistance to insecticides and drugs, the escalation of the human population with its attendant movement dynamics, shifts in land use patterns, and the erosion of the infrastructure underpinning public health efforts.
Notably, alterations in temperature, precipitation, humidity, and immunity levels also exert an influence on the transmission of malaria. The interplay of all these elements contributes to variations in adult mosquito densities and the maturation of the Plasmodium parasite within the mosquito host.
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Other Vector-borne Diseases - Mosquito-borne illnesses like chikungunya fever and dengue, along with parasitic conditions such as leishmaniasis, lymphatic filariasis, and onchocerciasis, as well as tick-borne diseases, might undergo alterations in their transmission dynamics or geographical spread due to the impacts of climate on the populations of relevant vectors. Additionally, climatic conditions could also play a role in the transmission of human plague, a bacterial disease transmitted by fleas, which are carried by rodents. The abundance and distribution of rodent populations are affected by temperature and rainfall, and these climatic elements, in conjunction with temperature and humidity's influence on flea survival and development, can collectively contribute to shifts in the occurrence of plague.
Similarly, murine typhus, another disease transmitted by fleas, might also exhibit analogous climate sensitivity. The behavior, prevalence, distribution, and capacity for virus transmission by vectors like mosquitoes are inherently shaped by temperature and precipitation.
Chikungunya and dengue, both arboviral diseases carried by the Aedes aegypti mosquito, are also prone to climate-related influences. Subsequently, the virus resurged in 2005 and has since rapidly expanded its reach, resulting in over a million reported cases, even without a standardized disease surveillance system34,35. Similarly, dengue has posed significant challenges, with India witnessing more than 50 dengue outbreaks since 196036. The behavior, prevalence, distribution, and capacity for virus transmission by vectors like mosquitoes are inherently shaped by temperature and precipitation
4. Fungal Infections: Elevating temperatures have facilitated the expansion of specific pathogenic fungi into previously uninhabitable regions characterized by lower temperatures. A notable instance is Valley fever, an affliction induced by a fungus thriving in the soil of hot and arid regions. This fungus has already extended its reach into regions like the Pacific Northwest. The consequences of this expansion can be dire, with the fungus capable of causing severe infections and even fatalities. Unfortunately, misdiagnosis and improper treatment are not uncommon for Valley fever cases. With the diminishing gap between environmental temperatures and human body temperatures, there exists a potential for the emergence of novel fungal diseases as fungi adapt to surviving within human hosts. Furthermore, climate change amplifies the susceptibility to natural disasters and flooding, events that can foster the proliferation of mold in residential environments. Certain molds possess the capacity to provoke lethal infections in the lungs and brain.
Conclusion
The shifting climate is inducing alterations in the prevalence and geographical spread of numerous infectious diseases. Evidenced by recent outbreaks of illnesses such as dengue, chikungunya, and West Nile virus in regions that were formerly unaffected by these diseases, these occurrences underscore the potential hazards linked to shifts in climate patterns, global trade, travel dynamics, and environmental changes.
